82 750 leaking gas from airbox hose

[longranger44]

So I bought my 82 750t a year ago and it has been running well since I bought it with the factory airbox setup, Always started immediately and idled well. I've not had the carbs apart and don't know their history, I assuming this bike sat for long periods of time since it has 18k miles. Well this week I went to start it and it turned over a bit and stopped and wouldn't crank anymore. I released the starter button and pushed it again and it would crank a couple times and then stop like the motor was stuck. I tried a third time and this time it started but would barely stay running, needing a lot more choke than usual and running like crap. it would die if I didn't give it at least around 10% throttle. As I backed it out of the spot I noticed a large wet spot of gas underneath and the tube coming from the airbox was wet inside and smelled of gas. So I turned it off and it continued leaking a small amount of gas from the airbox.
My first thought was maybe the main inlet needle valve is leaking on one of the carbs, but then I read that that shouldn't happen even with a bad needle valve because the petcock isn't supposed to feed fuel to the carbs in the run position with the motor off. Is this correct? I had never messed with the petcock before and when I tried to turn it it was very stuck, it could only be turned with a crescent wrench it was so stiff. I ordered a petcock rebuild kit but I'm wondering, Do I have multiple issues here? Thanks in advance!

 

[tom203]

The one year honeymoon is over! Hopefully , if you’re lucky ,just little issues need some attention .
With petcock in “on “ spot , gas will start flowing as you crank…if engine fails to run, gas could overflow a needle seat in one or more carbs….eventually this gets in airbox and down the drain hose.
First, check your charging system to find out why it failed it start…was battery dead? ..suddenly drained?
you may not need a new petcock , so check yours first. Rebuild kits are iffy

https://www.thegsresources.com/_forum/showthread.php?164993-Charging-System-QUICK-TEST

 

[longranger44]

The one year honeymoon is over! Hopefully , if you’re lucky ,just little issues need some attention .
With petcock in “on “ spot , gas will start flowing as you crank…if engine fails to run, gas could overflow a needle seat in one or more carbs….eventually this gets in airbox and down the drain hose.
First, check your charging system to find out why it failed it start…was battery dead? ..suddenly drained?
you may not need a new petcock , so check yours first. Rebuild kits are iffy

https://www.thegsresources.com/_forum/showthread.php?164993-Charging-System-QUICK-TEST

Haha well said, honeymoon over. I'm shocked it ran so well for so long to be honest. Well I don't think there was anything wrong with the charging system, to be honest it almost acted like it was hydrolocked although that didn't occur to me at the time. If the carb is leaking is it possible that gas could've leaked into a cylinder while sitting? It was on the centerstand on a pretty flat spot.
From my research it would seem that if the petcock was working correctly it wouldn't be able to keep leaking gas days after shutting off the motor, am I correct in that line of thinking? I had just filled the tank prior to this happening and it leaked out around a gallon of gas.

 

[Brendan W]

After long layups the shock of being run again can precipitate incipient failures.
There is a lot to be said for the old on off petcocks.
Did anyone mention that rebuild kits are iffy
Opening the old one and cleaning can sometimes make it better as was the case with my 850.
Try that first.

 

[rphillips]

It'd be a good idea to check to see if crankcase is over full of oil... and gas mix?

 

[longranger44]

After long layups the shock of being run again can precipitate incipient failures.
There is a lot to be said for the old on off petcocks.
Did anyone mention that rebuild kits are iffy
Opening the old one and cleaning can sometimes make it better as was the case with my 850.
Try that first.

Well the rebuild kit is in the mail but I can try cleaning the original one first and if that's all it needs I can send the kit back. I'm mainly wondering if a malfunctioning petcock alone could explain this? Or would it also have to be in conjunction with a bad needle valve (or sinking float) in the carb? Seems to me like there would have to be 2 points of failure here to cause this but I have an admittedly elementary understanding of the petcock system on this bike. Never dealt with one of these before.

 

[longranger44]

It'd be a good idea to check to see if crankcase is over full of oil... and gas mix?

I can certainly check, is it physically possible for a gas to make it into the engine from a leaking carb while it's just sitting there? Could it be both leaking backwards into the airbox and forwards into the engine simultaneously? Just changed the oil a few months ago so definitely want to get everything fixed in case I have to change the oil again so I don't waste another $30 in oil.

 

[tom203]

If petcock is working correctly, no fuel will get past petcock in “on or res” spot unless motor is running. If you put in “pr” spot ….and left in there too long…it could overfill fuel bowls with tired fuel needle seats. How long from your last “running well” ride till this event happen. If it usually starts right up, how come it didn’t this time?
This same stuff happened to me once last year and again this year …..I used prime and left bike on side stand briefly…I suspect tired needle seats on my carbs.

 

[Nessism]

Let's face it, your bike is 42 years old. Maintenance is required. Old rubber in the petcock deteriorates, same for the carb O-rings, and gas tanks can rust and send particles into the carbs.

There is no free lunch. Check the Newbie Mistakes thread link in my signature. Clean the tank, replace the petcock, and rebuild the carbs with new O-rings. That will get you half way home...

 

[longranger44]

If petcock is working correctly, no fuel will get past petcock in “on or res” spot unless motor is running. If you put in “pr” spot ….and left in there too long…it could overfill fuel bowls with tired fuel needle seats. How long from your last “running well” ride till this event happen. If it usually starts right up, how come it didn’t this time?
This same stuff happened to me once last year and again this year …..I used prime and left bike on side stand briefly…I suspect tired needle seats on my carbs.

I've never used the prime setting on the petcock, it's always been in the on position. I was going to turn it to prime when I started it this spring but it was so stiff that I couldn't turn it by hand so just left it alone. My only guess with the starting issue is that gas leaked into the combustion chamber while sitting and basically hydrolocked the motor and caused it to get stuck when the starter tried turning it. I had ridden it the week before and it ran fine, filled up the tank and the next time I went to start it like a week later, this happened.

 

[longranger44]

Let's face it, your bike is 42 years old. Maintenance is required. Old rubber in the petcock deteriorates, same for the carb O-rings, and gas tanks can rust and send particles into the carbs.

There is no free lunch. Check the Newbie Mistakes thread link in my signature. Clean the tank, replace the petcock, and rebuild the carbs with new O-rings. That will get you half way home...

I'm not at all opposed to doing maintenance, I've pretty much been working on this bike nonstop over the past year from the exhaust to the clutch to gaskets to putting everything back to stock from it's windjammer fairing setup, the carbs are one of the only things I haven't touched because it was running so well.
I looked into carb rebuild kits but the only ones I could find that were complete were aftermarket kits of questionable quality, I tried finding Mikuni kits but couldn't. Do the mikuni parts all need to be ordered separate? How much would one expect to pay to buy all the genuine parts to fully rebuild the carbs?

I'm reading through the newbie mistakes thread now it's quite a wealth of information.

 

[Nessism]

I'm not at all opposed to doing maintenance, I've pretty much been working on this bike nonstop over the past year from the exhaust to the clutch to gaskets to putting everything back to stock from it's windjammer fairing setup, the carbs are one of the only things I haven't touched because it was running so well.
I looked into carb rebuild kits but the only ones I could find that were complete were aftermarket kits of questionable quality, I tried finding Mikuni kits but couldn't. Do the mikuni parts all need to be ordered separate? How much would one expect to pay to buy all the genuine parts to fully rebuild the carbs?

I'm reading through the newbie mistakes thread now it's quite a wealth of information.

https://www.thegsresources.com/_for...2-mikuni-bs-cv-and-vm-o-ring-kits#post1703182

https://gsarchive.bwringer.com/mtsac/~cliff/storage/gs/Mikuni_BS-CV_Carburetor_Rebuild_Tutorial.pdf

 

[tom203]

Since this problem came on unexpectedly while the bike had been running well , I’d be real suspicious of your petcock, especially the stuff about gas in airbox and the hard-to-turn petcock lever. Test it and find out

Get some hoses that fit on petcock…one for the fuel outlet and one for the vacuum line to #2 carb. In “ON” spot no fuel should flow thru outlet hose …unless vacuum is applied thru the vacuum connection. If you carefully suck on vacuum line, fuel should flow, but it fuel is spotted in vacuum line , the petcock is no good. Don’t waste your time rebuilding it…just get new one! Georgefix guy sells two suzukigs versions…..one has more reserve capacity..I.e.you got slighty more fuel remaining when you switch over. Get new dowty washers under petcock mounting bolts…..common plumbing item.​

You might get lucky and find the culprit…and postpone carb fun. In any event, head Nessism’s advice and skip online carb rebuilding kits….you likely just need the o-ring stuff replaced.

 

[longranger44]

https://www.thegsresources.com/_for...2-mikuni-bs-cv-and-vm-o-ring-kits#post1703182

https://gsarchive.bwringer.com/mtsac/~cliff/storage/gs/Mikuni_BS-CV_Carburetor_Rebuild_Tutorial.pdf

So you don't recommend doing a new float valve needle and seat, just the orings?

 

[longranger44]

Since this problem came on unexpectedly while the bike had been running well , I’d be real suspicious of your petcock, especially the stuff about gas in airbox and the hard-to-turn petcock lever. Test it and find out

Get some hoses that fit on petcock…one for the fuel outlet and one for the vacuum line to #2 carb. In “ON” spot no fuel should flow thru outlet hose …unless vacuum is applied thru the vacuum connection. If you carefully suck on vacuum line, fuel should flow, but it fuel is spotted in vacuum line , the petcock is no good. Don’t waste your time rebuilding it…just get new one! Georgefix guy sells two suzukigs versions…..one has more reserve capacity..I.e.you got slighty more fuel remaining when you switch over. Get new dowty washers under petcock mounting bolts…..common plumbing item.​

You might get lucky and find the culprit…and postpone carb fun. In any event, head Nessism’s advice and skip online carb rebuilding kits….you likely just need the o-ring stuff replaced.

Sounds like a plan, how do I find this georgefix guy? I tried searching but just came up with people referencing him in posts

 

[Nessism]

So you don't recommend doing a new float valve needle and seat, just the orings?

I would inspect the float valves first. If the needle is worn, or if the spring is too weak to hold up the float, replace them. Keyster and real Mikuni float valves are by far the best. You will need float bowl gaskets, typically, and maybe the rubber pilot plugs. I often buy these kits for the float valves and gaskets. Add a full O-ring kit, because the rebuild kits O-rings don't fill out what's needed.

https://www.siriusconinc.com/products/detail/601

 

[tom203]

https://www.georgefixs.com

 

[longranger44]

Well finally got the new petcock on, while I had the tank off I checked the valve clearances and put in a new gasket for the cover. The old one was leaking and all of the bolts were loose, some backed off several turns. Took hours to clean all down in the spark plug valleys but got it done, hopefully that will solve my smoking problem. Side note, I learned that if you want to clean baked on crusty old oil, berrymans b12 cuts through it like butter. Super noxious though.

Anyway with the new petcock the issue is gone, it's running normally again. I'll fill the tank tonight and ride a bit and see if it stays that way. Eventually I'll pull the carbs and do o rings and clean everything but I'll probably make that a winter project as it tentatively seems to be running fine now. Thanks for all the replies and links!